Select Menu Item

Hello,

Having a little trouble getting a "menuitem" inside a "menu" which is inside a collapsible "panel".
There are several 'menu' panels which contain different menus and menu-items. The first panel defaults to "expanded" when the page renders so the menu-items are visible and he main content page loads.

After render, I want the menu-item for the main content page to be "selected" to show the user what page is visible. I don't know how to